Giovanni Pace

Pulsed Chemical Rocket with Green High Performance Propellants

PulCheR (Pulsed Chemical Rocket with Green High Performance Propellants) is a new propulsion concept in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses, reproducing the defence mechanism of a notable insect: the bombardier beetle. The radical innovation introduced by PulCheR is the elimination of any external pressurizing system even if the thruster works at high pressure inside the combustion chamber. At each pulse, pressurization of the combustion chamber gases takes place due to the decomposition or combustion reaction, and the final pressure is much higher than the one at which the propellants are stored. The weight of the feeding system is significantly reduced because the propellants are fed at low pressure, and there is no need for turbopumps, high pressure propellant tanks or gas vessels. The feed pressure becomes independent on the chamber pressure and the performance degradation typical of the blow down mode in monopropellant thrusters can be avoided. The PulCheR concept is able to substitute many currently used propulsion systems for accessing space in both mono and bipropellant configurations. The preliminary assessment of this new propulsion concept has been investigated using green propellants with potential similar performance to the current stateof-the-art for monopropellant and bipropellant thrusters.

Geometry Effects on Flow Instabilities of Different Three-Bladed Inducers

The paper presents the results of an activity carried out on a three-bladed inducer and compares the experimental data from other similar inducers. All the inducers considered in the present study have been designed by means of the simplified analytical model recently developed by some of the authors. The main effects of different geometrical solutions on hydraulic performance and flow instabilities of the pumps under noncavitating and cavitating conditions are presented in the paper.

Experimental Characterization of the Dynamic Transfer Matrix of Cavitating Inducers

The present paper illustrates and discusses the first results of the characterization of the dynamic transfer matrix of cavitating turbopumps by means of a series of forced-vibration tests carried out on a high-head three-bladed inducer in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at Alta, Pisa, Italy. The flow has been excited by vertically vibrating with adjustable frequency and intensity the free-surface tank used to close the loop of the suction and discharge lines of the inducer. The pressure and flow rate fluctuations for the determination of the dynamic transfer matrix have been obtained from unsteady pressure measurements at suitable locations on the inlet/outlet lines of the inducer. Two loop configurations with different inlet/outlet impedances to/from the test inducer have been used in order to obtain at each excitation frequency a set of four linearly independent measurements for the detetermination of the four elements of the dynamic transfer matrix. The preliminary results are in qualitative agreement with the scant data available in the literature for comparable inducers.

Study on Hydraulic Performances of a 3-Bladed Inducer Based on Different Numerical and Experimental Methods

The hydraulic performances of a 3-bladed inducer, designed at Alta, Pisa, Italy, are investigated both experimentally and numerically. The 3D numerical model developed in ANSYS CFX to simulate the flow through the inducer and different lengths of its inlet/outlet ducts is illustrated. The influence of the inlet/outlet boundary conditions, of the turbulence models, and of the location of inlet/outlet different pressure taps on the evaluation of the hydraulic performance of the inducer is analyzed. As expected, the predicted hydraulic performance of the inducer is significantly affected by the lengths of the inlet/outlet duct portions included in the computations, as well as by the turbulent flow model and the locations of the inlet/outlet pressure taps. It is slightly affected by the computational boundary conditions and better agreement with the test data obtained when adopting the turbulence model. From the point of the pressure tap locations, the pressure rise coefficient is much higher when the inlet/outlet static pressure taps were chosen in the same locations used in the experiments.

Experimental Validation of a Reduced Order for Radial Turbopump Design

The paper illustrates the experimental validation of the reduced order model recently developed at Alta, Pisa (Italy), for the simultaneous and preliminary geometrical definition and non-cavitating performance prediction of centrifugal turbopumps. The proposed model has been employed to size and design the test machine, named VAMPIRE and equipped with a six-bladed radial impeller, a vaneless diffuser and a single-spiral volute. The pumping and suction performance of the machine have been determined in a series of tests in Alta’s Cavitating Pump Rotordynamic Test Facility (CPRTF). The measured pumping characteristic proved to be in excellent agreement with the model predictions, thus effectively validating the design model. In addition, the experimental determination of the pump’s cavitation characteristic is fully consistent with the expected suction performance of comparable machines, confirming the capability of the proposed model to generate hydrodynamically efficient turbopump designs.

Inducer and Centrifugal Pump Contributions to the Rotordynamic Fluid Forces Acting on a Space Turbopump

Hawaii, Honolulu April 10-15, 2016 Abstract The fluid induced rotordynamic forces acting on a whirling space turbopump composed by an inducer and a radial impeller have been compared to the same forces measured on each single component of the turbomachine (i.e. on the inducer and on the radial impeller). The experimental campaign has been carried out in cold water at design and offdesign conditions (80%, 100% and 120% of the design flow rate) both in non-cavitating and cavitating regimes. The paper illustrates the different trends of the rotordynamic forces on the axial and radial pumps and highlights their contributions on the overall turbomachine. At positive whirl ratios, the behavior of the inducer is dominant while, at negative ones, both the pumps show the same trends in such a way that the overall behavior is roughly the sum of each single component.

Analysis of Flow Instabilities on a Three-Bladed Axial Inducer in Fixed and Rotating Frames

The paper describes results of recent experiments carried out under similarity conditions in the Cavitating Pump Rotordynamic Test Facility for the dynamic characterization of cavitation-induced flow instabilities as simultaneously observed in the stationary and rotating frames of a high-head, three-bladed axial inducer with tapered hub and variable pitch. The flow instabilities occurring in the eye and inside the blading of the inducer have been detected, identified and monitored by means of the spectral analysis of the pressure measurements simultaneously generated in the absolute and relative frames by multiple transducers mounted on the casing near the impeller eye and on the inducer hub along the blade channels. The comparison of the results obtained in the two reference frames over a wide range of flow coefficients and cavitation numbers contributed to shed some light on the complex dynamic interactions between the cavitation-induced instabilities in the eye and in the blade channels of typical high-head inducers.

An Introduction to Flow-Induced Instabilities in Rocket Engine Inducers and Turbopumps

The article reviews the main forms of flow-induced instabilities detected in the liquid propellant turbopumps systems of modern rocket engines, with special reference to rotating stall, rotating cavitation, cavitation surge and higher order surge modes, illustrating their characteristics, origin and damage potential.

An Introduction to Cavitation in Inducers and Turbopumps

After a brief review of the fundamental aspects of cavitation relevant to the operation of high-performance inducers and turbopumps, the article summarizes their application to the analysis of pumping systems, illustrates the scaling of cavitation phenomena from model tests to full-scale operation, describes the occurrence of flow-induced instabilities in turbomachinery, and introduces the concepts of static and dynamic instability of pumping systems and their generalization to cavitating turbopump systems.

On the Preliminary Design and Performance Prediction of Centrifugal Turbopumps—Part 1

A reduced-order model for the preliminary design and performance prediction of radial turbopumps is illustrated. The model expresses the 3D, incompressible, inviscid, irrotational flow through helical blades with slow axial variations of their pitch and backsweep angles by superposing a 2D axial vorticity correction to a fully guided forced vortex flow with axisymmetric stagnation velocity in the meridional plane. Application of the relevant governing equations allows for the closed-form definition of the impeller geometry and flowfield in terms of a reduced number of controlling parameters. Mass and momentum conservations are used for coupling the flow leaving the impeller with the 2D reduced-order models of the flow in the diffuser and/or the volute, as well as for the evaluation of the mixing losses in the transfer between successive components of the machine. This information completes the geometric definition of the turbopump and determines its ideal noncavitating performance in accordance with the resulting flowfield. As a consequence of the neglect of viscous effects, the slip factor predicted by the present model exceeds those obtained from theoretical/semi-empirical formulas reported in literature for centrifugal pumps, but correctly captures their trend.